This invention relates to a sheet feeder device, particularly for offset printing machines.
Known pneumatic sheet feeder devices transfer the paper sheets from a pile to the feeder which feeds the sheets in overlapped arrangement to the printing unit. Some feeder devices are arranged in such a way, that a special mechanism can be connected with the feeder device which enables the feeding of paper sheets of large size or of special forms.
The scope of the present invention is to provide a sheet feeder device, where the paper sheets are arranged in a pile and are transferred from the pile by means of a pneumatic sucker head to a transport device, whereby the feeder device enables the feeding also of letter envelopes or other cross-formed letters which are piled longitudinally or transversely. The same elements are used for the straightening of the paper sheet as well as for the forming of the pile of sheets. Further, the device according to the invention provides the possibility to replace the guide rollers with rollers which correspond according to the thickness and toughness of envelopes to be printed. The guide rollers can be easily and quickly adjusted according to the size of the paper sheets.
Other sheet feeder devices are known, to which a special accessory device can be connected, to enable the feeding also of piled envelopes or of similar material. This device works in such a way, that the envelopes arranged in a pile which is located in the accessory device, are pushed by a mechanical friction element to the transporting device and to the printing unit. The disadvantage of this device is in that the printing machine in this case has to be provided with a special accessory device for the feeding of envelopes which again has to be dismantled from the machine, when a different kind of printing work is to be done on the machine.
Other known devices which enable the feeding of letter envelopes or of other envelopes are arranged in such a way, that pneumatic suckers take the envelopes at their leading edge from the pile and transfer one envelope after the other to the transport device, with an appropriate distance being allowed between envelopes. A disadvantage of this feeder device is that the action of feeding envelopes limits the printing output of the printing machine, whereby the transport of envelopes, which are of small size, is not accurate.